The present disclosure relates to a nonaqueous electrolyte and to a nonaqueous electrolyte battery. In more detail, the present disclosure relates to a nonaqueous electrolyte containing a nonaqueous solvent and an electrolyte salt and to a nonaqueous electrolyte secondary battery using the same.
In recent years, portable electronic appliances such as a camera-integrated VTR (video tape recorder), a mobile phone and a laptop personal computer have widely spread, and it is strongly demanded to realize downsizing, weight reduction and long life thereof. Following this, the development of batteries as a power source, in particular, secondary batteries which are lightweight and from which a high energy density is obtainable is advanced.
Above all, lithium ion secondary batteries utilizing intercalation and deintercalation of lithium (Li) for a charge/discharge reaction are largely expected because a high energy density is obtainable as compared with lead batteries and nickel-cadmium batteries. Such a lithium ion secondary battery is provided with an electrolyte together with a positive electrode and a negative electrode, and the development is extensively advanced for the purpose of enhancing various performances of nonaqueous electrolyte secondary batteries.
In particular, laminated batteries using an aluminum laminated film for a package member have a large energy density because of their light weight. However, in the laminated batteries, in the case of using an electrolyte composed of a fluid electrolyte such as existing electrolytic solutions, a problem such as liquid leakage following deformation of the package member to be caused due to expansion of the battery is easily generated. For that reason, as a method for solving this problem, batteries using a non-fluid electrolyte such as solid electrolytes and gel electrolytes are watched. The batteries using a non-fluid electrolyte have such advantages that they are low in a concern of liquid leakage, so that the safety is enhanced; and that a lightweight and thin material such as an aluminum laminated film can be used for the package member.
Meanwhile, following a more increase of the energy density of nonaqueous electrolyte secondary batteries, in order to increase the charge/discharge characteristics of the battery, it is necessary to make a delivery speed of ions between a positive electrode and a negative electrode fast as far as possible. For achieving this, it is necessary to make it easy to cause the mass transfer by diffusion by increasing an ion conductivity of the electrolyte or decreasing a viscosity of the electrolyte. However, in secondary batteries using a non-fluid electrolyte, such characteristics are of a problem. That is, in electrolytic solutions which are a existing fluid electrolyte, the transfer of ions in the liquid is easy, whereas in non-fluid electrolytes, the ion conductivity of the electrolyte is reduced because of its viscosity. In order to improve these performances, Patent Documents 1 to 3 (JP-A-08-045545, JP-A-2002-329528 and JP-A-10-189042) propose techniques for stabilizing the electrode surface by forming a coating film which is called an SEI (solid electrolyte interface) coating on the electrode at the time of charge/discharge at the beginning of use of the battery.
By such an additive-containing electrolyte constitution, an improvement in the battery characteristics is found. However, as to the foregoing problem of the electrolyte, in the case where it is contrived to realize a higher capacity in the future, a much more enhancement is demanded. In particular, this phenomenon becomes conspicuous in the use over a long period of time. As a result, not only deterioration of the storage characteristic and rate characteristic is caused due to a lowering of the ion conductivity, but in the case of using a shape-changeable package member such as an aluminum laminated film, deformation of the battery such as an increase of the battery thickness becomes problematic.
In the electrolytic solutions containing an unsaturated group-containing cyclic compound such as vinylene carbonate (VC), as proposed by the foregoing patent documents, by covering the surface of a negative electrode with a coating film, side reactions caused on the surface of the negative electrode, such as decomposition of a solvent, can be suppressed. For that reason, a lowering of the initial capacity and the like are improved. For such a reason, in particular, vinylene carbonate (VC) is widely used as an additive of the electrolytic solution.